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Class 


History  and  Development  of  the  De- 
position of  Copper  Ferrocyanide 
Membrane  by  the  Electro- 
lytic Method 


DISSERTATION 


SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES  OF 

THE  JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY 

WITH  THE  REQUIREMENTS  FOR  THE  DEGREE 

OF  DOCTOR  OF  PHILOSOPHY 


BY 

CHESTER  NEWTON  MYERS 

BALTIMORE 
1910 


EASTON,   PA.: 
ESCHRNBACH  PRINTING  CO. 

I9II 


History  and  Development  of  the  De- 
position of  Copper  Ferrocyanide 
Membrane  by  the  Electro- 
lytic Method 


DISSERTATION 


SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES  OF 

THE  JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY 

WITH  THE  REQUIREMENTS  FOR  THE  DEGREE 

OF  DOCTOR  OF  PHILOSOPHY 


BY 

CHESTER  NEWTON  MYERS 

BALTIMORE 
1910 


EASTON,  PA.: 

ESCHBNBACH  PRINTING  Co. 
1911 


ACKNOWLEDGMENT. 

The  author  desires  to  express  grateful  acknowledgment 
to  Professor  Morse  for  his  kindly  assistance  and  experienced 
supervision  in  this  investigation.  His  inspiration  and  valu- 
able instruction  in  careful  manipulation  call  for  appreciative 
recognition.  To  President  Remsen  for  his  valuable  instruc- 
tion in  the  lecture  room  and  the  pleasant  memories  connected 
with  his  lectures  are  due  the  gratitude  and  recognition  of 
the  author.  No  less  are  Professors  Acree,  Jones,  Ames 
and  Bliss  worthy  of  recognition.  The  author  also  wishes 
to  use  this  opportunity  of  expressing  thanks  to  the  earlier 
co-workers  of  Prof.  Morse  for  valuable  suggestions  obtained 
from  their  publications.  To  Dr.  Holland  for  his  untiring 
assistance  and  suggestions,  great  appreciation  is  due. 


History  and  Development  of  the  Deposition  of 

Copper  Ferrocyanide  Membrane  by  the 

Electrolytic  Method* 


It  is  quite  unnecessary,  in  giving  an  historical  account 
of  the  work  done  on  semipermeable  membranes,  to  mention 
more  than  briefly,  the  work  and  investigations  of  Pfeffer, 
the  theoretical  conclusions  of  van't  Hoff  founded  upon 
Pfeffer's  determinations,  the  results  of  Tammann,  Ham- 
burger, and  De  Vries,  men  working  upon  van't  Hoff's  brilliant 
conclusions.  Such  were  the  investigations  and  conclusions 
which  showed  the  scientific  world  the  great  importance  of 
the  subject  with  which  we  are  now  dealing.  Notwithstanding 
the  almost  insurmountable  difficulties  of  the  work,  later 
progress  has  corresponded  to  these  brilliant  beginnings. 

No  work  comparable  to  that  of  Pfeffer's  has  ever  been 
done,  following  the  methods  of  this  investigator,  but  a  new 
method  has  come  to  the  front,  replaced  an  old  one,  given 
results  which  are  in  a  class  by  themselves  for  accuracy  and 
originality  of  determination.  This  practical  method  of 
membrane  deposition  and  its  application  to  the  work  was 
devised  by  Morse  and  Horn,  improved  upon  by  Morse  and 
his  later  co-workers.  To  them,  we  owe  the  first  ideas  of 
electrolytic  deposition  of  the  semipermeable  membrane 
in  the  walls  of  a  porous  cup. 

In  the  original  article  of  Morse  and  Horn,  they  state  the 
object  they  had  in  mind  in  the  following  words :  "It  occurred 
to  the  authors  that  if  a  solution  of  copper  salt  and  one  of 
potassium  ferrocyanide  are  separated  by  a  porous  wall 
which  is  filled  with  water,  and  a  current  is  passed  from  an 
electrode  in  the  former  to  another  electrode  in  the  latter 
solution,  the  copper  and  the  ferrocyanogen  ions  must  meet 
in  the  interior  of  the  wall  and  separate  as  copper  ferrocyanide 
at  all  the  points  of  meeting,  so  that  in  the  end  there  should 
be  built  up  a  continuous  membrane  well  supported  on  either 


222272 


6 

side  by  the  material  of  the  wall."  Such  were  the  first  con- 
ceived ideas  in  the  progress  of  the  methods  of  membrane 
formation. 

The  first  problem  which  confronted  the  efforts  of  this 
early  work  was  a  method  of  effectively  removing  the  air 
from  the  porous  cups  which,  in  themselves,  furnished  but 
a  poor  means  of  supporting  the  copper  ferrocyanide  mem- 
brane. The  purpose  of  removing  the  air  from  the  walls 
of  the  cell  is  obviously  to  overcome  the  interference  in  the 
formation  of  a  sound  and  homogeneous  membrane.  The 
investigators  made  use  of  the  strong  endosmose  which  ap- 
pears, when  a  current  is  passed  through  a  porous  wall,  sepa- 
rating two  liquid  substances.  The  Morse-Horn  method 
of  removing  the  air  from  the  walls  of  these  porous  cups, 
consisted  in  the  use  of  a  boiled  solution  of  potassium  sulphate 
containing  about  five-tenths  of  a  gram  of  salt  in  a  liter  of 
water.  This  sulphate  solution  is  placed  both  in  the  interior 
of  the  porous  cup  and  in  the  jar  in  which  the  cup  sits.  On 
passing  the  current  between  the  electrodes  in  the  direction 
of  the  electrode  within,  the  liquid  in  the  cup  rises  with  a 
sufficient  rapidity  to  increase  with  the  dilution  of  the  solution 
and  with  the  intensity  of  the  current.  As  the  liquid  is  carried 
along  by  the  electric  current,  the  air  is  bodily  swept  along 
with  the  water  to  the  interior  of  the  cell  and  thence  out  of 
the  siphon. 

The  electrodes  used  for  this  work  are  platinum.  The 
inner  electrode  is  fastened  to  the  platinum  wire  which  passes 
through  the  rubber  stopper.  This  rubber  stopper  contains 
a  funnel  which  admits  solution  to  the  interior  of  the  cell 
and  a  side  tube  which  serves  as  an  outlet  and  part  of  the 
siphon.  As  this  endosmose  takes  place,  it  is  found  that 
water  and  air  pass  through  very  rapidly  at  first.  The  sul- 
phate is  added  to  the  jar  occasionally,  and  the  electrolysis 
is  continued  until  about  three  hundred  cc.  of  the  sulphate 
has  passed  out  through  the  siphon.  This  is  found  to  be 
sufficient  to  remove  all  air  that  may  have  been  included 
within  the  walls  of  the  cell.  According  to  this  method, 
the  cells  were  then  placed  in  a  large  volume  of  distilled  water 


to  remove  the  salt  that  had  accumulated  in  the  walls  of  the 
cell. 

''To  form  the  membrane,  the  wet  cup  was  placed  in  a 
beaker  and  surrounded  with  an  electrode  of  sheet  copper, 
which  completely  encircled  it.  The  other  electrode — the 
one  within  the  cup — was  of  platinum.  After  fixing  the 
electrodes  and  connecting  with  a  dynamo,  so  that  the  current 
should  begin  to  flow  the  instant  the  liquids  touched  the 
opposite  walls  of  the  cup,  the  copper  solution  (N/io  or 
N/s  sulphate)  and  that  of  potassium  ferrocyanide  (N/io 
or  N /  5)  were  introduced  as  nearly  simultaneously  as  possible. 
At  first,  there  is  considerable  endosmose  in  the  direction 
of  the  current,  i.  e.,  from  the  copper  solution  into  that  of  the 
ferrocyanide,  but  no  copper  has  ever  been  found  to  enter 
the  cup,  neither  have  any  of  the  ferrocyanogen  ions  made 
their  way  into  the  copper  solution.  The  resistance  usually 
rises  quite  rapidly,  reaching  in  extreme  cases  three  thousand 
ohms  within  an  hour,  while  the  endosmose  decreases  corre- 
spondingly. The  most  rapid  rise  in  resistance  is  observed 
in  the  less  porous,  hard  burned  cells.  In  softer  and  more 
porous  ones,  the  resistance  may  not  exceed  two  hundred 
to  three  hundred  ohms  within  an  hour;  and  after  a  time, 
in  such  cases,  the  resistance  begins  to  fall,  owing,  apparently, 
to  the  action  of  the  accumulated  alkali  upon  the  membrane. 
If  the  solution  of  ferrocyanide  in  the  cell  is  then  replaced 
by  a  fresh  one,  the  resistance  begins  to  rise  again."  Such 
were  the  observations  of  Morse  and  Horn  in  their  original 
paper. 

In  the  earlier  work  it  was  regarded  improbable  that  the 
osmotic  pressure  of  concentrated  solutions  could  be  measured 
because  a  satisfactory  membrane  could  not  be  deposited 
by  electrolysis.  The  difficulty  which  manifested  itself 
was  in  the  fact  that  the  walls  of  the  cell  may  contain  cavities 
of  such  size  as  to  interfere  with  the  best  results  of  membrane 
formation,  in  that  it  is  necessary  for  a  "key"  to  attach  the 
membrane  to  and  then  to  pack  sufficiently  a  membrane 
of  considerable  volume,  attached  only  at  a  few  points.  During 
this  stage  of  the  investigation  it  was  found  that  the  walls 


8 

of  the  cell  must  be  very  compact  to  start  with,  then  this  cell 
should  be  burned  so  that  it  was  very  hard.  A  cell  of  close 
texture,  however,  is  found  to  be  an  essential  feature  for  a 
cell  of  good  quality. 

Having  thus  obtained  a  cell  of  this  character,  the  next 
step  is  to  prepare  it  for  the  membrane-forming  process. 
The  method,  formerly  employed,  consisted  in  passing  a  solu- 
tion of  potassium  sulphate  through  the  cell  and  then  by 
endosmose,  allowing  water  to  remove  any  accumulated 
salt  from  the  walls  of  the  cell.  This  endosmose  is  continued 
until  the  liquid  conducts  the  current  very  poorly.  The 
cell  is  now  ready  for  membrane  deposition.  To  deposit  the 
membrane,  the  following  procedure  is  employed:  A  long 
platinum  rod,  which  serves  as  the  cathode,  is  lowered  into 
the  cell,  and  a  cylinder  of  copper  in  copper  sulphate  solution 
is  used  as  the  anode.  Into  the  cell,  there  is  inserted  a  siphon, 
which  reaches  nearly  to  the  bottom  of  the  cup.  The  purpose 
of  this  siphon  is  to  remove  the  liquid  from  time  to  time 
in  order  to  prevent  the  accumulation  of  alkali,  which  is  be- 
lieved to  be  injurious  to  the  membrane.  For  this  deposition, 
an  N / 10  ferrocyanide  solution  and  an  N/io  copper  sulphate 
solution  are  introduced  into  the  cup,  the  former  being  placed 
in  the  interior  of  the  cup,  the  latter  being  placed  in  the  jar 
in  which  the  cup  rests.  During  the  process  of  actual  measure- 
ment, potassium  ferrocyanide  and  CuSO4  are  used  in  the 
».  solutions  for  the  purpose  of  mending  the  momentary  ruptures 
in  the  membrane,  caused  by  the  increasing  pressure. 

Up  to  this  time,  membranes  of  copper  ferrocyanide  had  re- 
ceived most  attention,  but  at  this  stage  of  the  work  further  re- 
search in  regard  to  membranes  was  carried  on.  It  was  now 
found  that  the  electrolytic  method  is  well  adapted  to  the  de- 
position upon  or  within  the  walls  of  a  cell  of  nearly  every  kind 
of  precipitate  which  can  be  formed  from  electrolytes  in 
solution.  The  ferrocyanides  of  tin,  zinc,  cadmium,  man- 
ganese and  uranyl;  phosphates  of  the  iron  (trivalent),  copper, 
and  uranyl;  hydroxides  of  aluminium  and  iron  (trivalent); 
cobalti  cyanides  of  cobalt,  nickel,  iron  (bivalent),  copper, 
zinc,  cadmium,  and  manganese  were  shown  to  manifest 


osmotic  activity  to  a  promising  degree.  These  membranes 
should  possess  the  properties  of  insolubility,  firm  consistency, 
chemical  inertness,  permanency,  and  most  of  all  osmotic 
activity  and  semipermeability .  These  membranes,  for  the 
most  part,  possess  these  properties  to  a  greater  or  less  degree. 
It  was  found  that  cells  of  various  textures  were  needed  for 
different  membranes. 

As  the  progress  of  the  work  advanced,  it  was  found  ad- 
visable to  use  one-tenth  normal  solutions  of  copper  sulphate 
and  potassium  ferrocyanide  to  deposit  the  membrane.  In 
membranes  of  this  class,  it  is  found  that  alkali,  which  accu- 
mulates during  the  process  of  electrolysis,  must  be  removed, 
owing  to  the  deleterious  effects  upon  the  membranes.  How- 
ever, it  was  found  that,  in  the  case  of  the  cobalti  cyanide 
membranes,  a  little  acetic  acid  can  be  used  to  prevent  the 
accumulation  of  alkali.  It  was  considered  a  too  hazardous 
performance  in  the  case  of  other  membranes  which  showed 
great  activity. 

Voltages  ranging  from  no  volts  to  250  were  tried,  but 
upon  experimental  evidence,  it  was  found  that  voltages 
between  no  and  120  gave  more  satisfactory  results  than 
any  other  voltages.  A  greenish-black  deposit  was  observed 
at  higher  voltages,  instead  of  the  formation  of  the  cyanide 
membrane.  The  probable  explanation  is  the  decomposi- 
tion of  the  membrane  of  copper  ferrocyanide  which  is  first 
formed.  It  is  noticed  that,  when  the  circuit  is  first  closed, 
the  resistance  is  very  high  in  some  cases,  due  to  the  fact  that 
there  is  an  absence  of  the  electrolyte  in  the  cell  wall — pure 
water.  Soon,  however,  the  current  increases  for  a  short 
time  but  falls  rapidly  after  having  reached  this  maximum. 
It  is  a  result  of  experience  that,  if  any  further  increase  in 
current  occurs,  the  cell  should  be  taken  down.  To  some 
extent  the  probable  excellence  of  a  cell  is  determined  by 
its  conduct  during  the  membrane-forming  process.  The 
cell  is  now  taken  down,  washed,  and  placed  in  distilled  water 
before  setting  up  for  measurement. 

Such  has  been  the  experimental  stages  through  which 
the  investigations  passed.  A  description  of  the  work  of 


10 

preparing  a  cell  which  gave  measurements  in  which  consider- 
able reliance  might  be  placed,  is  now  in  order.  The  treat- 
ment previously  described,  was  given  the  cells  and  the 
deposition  of  the  membrane  begun.  It  was  noticed  that 
the  first  membrane  deposited  rarely  gave  the  highest  pressure 
which  is  known  to  be  normal  for  that  solution.  It  thus 
becomes  evident  that  a  good  membrane  must  be  built  up 
gradually.  To  do  this,  certain  definite  methods  must  be 
followed.  A  membrane  is  deposited;  then  it  is  rendered 
more  compact  by  subjecting  it  to  pressure  de\  eloped  by  a 
sugar  solution.  It  is  taken  down,  washed,  subjected  to 
the  membrane-forming  process  to  repair  any  of  the  ruptures 
which  have  been  produced  and  finally  set  up  for  packing 
again.  This  is  repeated  for  a  time  sufficient  to  produce  a 
compact,  non-leaking  membrane.  This  alternating  rup- 
turing and  packing  is  continued  until  the  ruptures  are  very 
small.  At  this  stage  another  method  of  repair  and  mending 
is  used.  This  is  a  simultaneous  rupturing  and  mending 
process  in  which  copper  sulphate  on  the  outside  and  potas- 
sium ferrocyanide  on  the  inside,  in  osmotically  equivalent 
amounts  are  used.  This  process  takes  place  during  actual 
measurement.  A  cell  failing  to  develop  high  pressure  is 
probably  due  to  leakage,  for  a  solution  in  a  cell  with  a  leaking 
membrane  may  exhibit  a  nearly  constant  pressure  for  a 
long  time,  thus  giving  one  who  has  had  little  experience 
with  membranes  or  one  who  gives  them  careless  attention, 
the  impression  that  he  is  measuring  true  maximum  pressures. 
Semipermeable  membranes  are  probably  inversely  related 
to  the  molecular  weights  of  the  substances  whose  pressures 
are  measured  (i.  e.,  a  membrane  may  not  leak  with  cane  sugar 
but  leaks  very  readily  with  glucose).  Even  in  leaking 
cells,  satisfactory  measurements  might  be  obtained  by  the 
differential  method.  The  differential  method  consists  in 
allowing  the  membrane  to  develop  a  constant  pressure 
and  then  determine  the  concentration  of  the  solution  within 
and  without  the  cell.  This  gives  sufficient  data  for  a  correct 
interpretation. 

The  difficulties  attending  the  work  were  now  increased 


II 

by  the  appearance  of  a  formidable  assailant  which  mani- 
fested itself  in  the  form  of  a  minute  vegetable  organism 
known  as  penicillium.  The  development  of  ferments  and 
the  chemical  changes  attending  their  growth  has  been  studied 
only  to  a  limited  extent.  It,  therefore,  was  necessary  to 
obtain  an  efficient  means  of  destroying  these  organisms 
which  are  extraneous  in  the  development  of  maximum 
osmotic  pressure.  Necessity  demanded  that  this  poison 
should  be  effective  in  such  small  quantities  that  the  pressure 
of  the  solutions  should  not  be  effected.  Secondly,  it  must 
not  act  chemically,  or  otherwise  upon  the  membrane,  and 
lastly,  is  must  not  act  chemically  upon  the  solution.  Possess- 
ing these  three  fundamental  characteristics,  it  should  also 
be  able  to  prevent  alcoholic  fermentation.  It  thus  appears 
that  substances  of  an  alkaline  or  acid  nature  were  excluded 
from  the  outset.  A  series  of  experiments  was  undertaken 
with  phenol,  salicylic  acid,  thymol,  hydrocyanic  acid,  chloro- 
form and  potassium  cyanide,  although  no  good  results  could 
be  expected  from  the  last.  In  the  case  of  phenol,  salicylic 
acid  and  potassium  cyanide,  a  retardation  in  the  growth 
was  observed.  However,  a  vigorous  growth  appeared 
later  when  penicillium  was  placed  in  a  sterilized  Pasteur's 
solution.  Deleterious  effects  on  the  membrane  were  also 
noticed.  It  is  possible  that  hydrocyanic  acid  might  be  used 
but  the  inconveniences  accompanying  its  use  eliminated 
it  from  consideration.  Thymol  was  the  only  substance 
which  seems  to  fully  meet  the  demands.  Thymol  is  very 
insoluble  in  water  and  a  solution  of  one  thousandth  normal 
is  found  to  be  sufficiently  concentrated  to  poison  all  growths 
of  this  kind. 

Turning  to  more  recent  work  on  membranes  and  the 
porous  cups  in  which  they  are  deposited,  it  can  be  said  that 
the  method  is  essentially  the  same  as  that  of  the  earlier 
workers.  A  cell  is  prepared  for  the  membrane-forming 
process  in  the  following  way:  A  five- thousandth  normal 
solution  of  lithium  sulphate  is  placed  in  the  cell  and  also 
in  the  jar  in  which  the  cell  rests.  It  is  connected  to  an  elec- 
tric circuit  with  electrodes  of  the  same  kind  as  previously 


12 

described.  The  air  is  then  driven  out  of  the  cell  wall  by 
the  endosmose  of  the  sulphate  solution  which  is  elect roly zed. 
Lithium  sulphate  is  used  in  place  of  potassium  sulphate 
for  the  reason  that  the  lithium  ion  is  surrounded  by  a  greater 
endosmose  than  the  potassium  ion.  The  electrodes  for  this 
work  are  made  of  platinum.  The  anode  consists  of  a  cylinder 
of  platinum  of  sufficient  size  to  surround  the  lower  portion 
of  the  cell.  The  cathode  is  a  smaller  platinum  cylinder 
which  is  fastened  to  a  platinum  wire  passing  through  the 
rubber  stopper  at  the  same  place  as  the  funnel  which  ad- 
mits solution  into  the  cell.  The  funnel  is  of  sufficient  length 
to  reach  nearly  to  the  bottom  of  the  cell,  thus  carrying  fresh 
solution  to  the  bottom  of  the  cell  and  forcing  the  old  solution 
upward  and  outward  through  the  siphon.  The  siphon  is 
formed  by  a  second  glass  tube  which  passes  through  the 
rubber  stopper  but  bent  at  right  angles  to  the  funnel.  These 
electrodes  are  now  connected  to  a  no  volt  circuit  and  the 
air  is  carried  out  by  the  large  lithium  ion. 

The  cell  is  placed  in  distilled  water  to  remove  any  lithium 
salt  that  may  have  accumulated  in  the  walls.  The  cell  is 
now  set  up  in  the  circuit,  using  distilled  water  and  the  re- 
mainder of  the  lithium  salt  is  electrolyzed  in  the  same  manner 
as  the  air  was  removed,  water  being  used  instead  of  a  sul- 
phate solution.  This  electrolysis  is  continued  until  a  mini- 
mum current  is  obtained.  This  minimum,  in  most  cases, 
reaches  about  two  ten-thousandths  of  an  ampere.  From 
this  time  on  the  cell  is  never  exposed  to  the  air  for  any  length 
of  time,  nor  is  the  unglazed  portion  ever  handled  by  the  worker. 
These  precautions  are  manifestly  necessary. 

The  real  work  of  depositing  the  membrane  is  now  ready 
to  begin  and  a  longer  process  is  before  the  investigator. 
For  the  deposition  of  membranes,  a  tenth-normal  solution 
of  copper  sulphate  is  used  as  the  solution  on  the  exterior 
and  a  tenth-normal  solution  of  potassium  ferrocyanide  is 
used  around  the  cathode.  The  cathode  is  a  platinum  cylinder 
and  the  anode  is  a  copper  cylinder  in  copper  sulphate.  Peni- 
cillium  thrives  very  vigorously  in  copper  sulphate  and  at 
this  point  it  is  necessary  to  take  very  great  precautions. 


13 

If  a  new  solution  of  copper  sulphate  in  water  is  used,  the 
deposition  goes  on  satisfactorily.  It  is  not  always  convenient 
to  put  a  new  solution  of  sulphate  in  the  cup  each  time  and  to 
avoid  the  growth  of  penicillium  it  is  found  advantageous 
to  make  the  copper  sulphate  solutions  in  thymol  water  of 
a  concentration  of  one- thousandth  normal.  Thymol  seems  to 
effect  electrolysis  in  no  way  and  does  not  interfere  with  the 
deposition  of  the  membrane.  It  prevents  any  growth  of 
penicillium.  The  jar  in  which  the  copper  sulphate  solu- 
tion is  placed  is  held  by  means  of  suitable  mechanical  devices 
in  a  constant  temperature  bath,  and  the  cell  is  allowed  to 
dip  into  the  copper  sulphate  solution  to  a  short  distance 
above  the  beginning  of  the  glazed  portion.  The  electrodes 
are  arranged  so  that  they  are  connected  to  fixed  binding  posts 
which  are -easily  put  in  circuit  carrying  current  and  an  am- 
meter for  recording  the  current  passing  through  the  cell. 
Each  time  the  cell  is  set  up  for  deposition  of  membrane, 
the  voltage  is  taken  and  the  current  read  every  fifteen  min- 
utes. This  is  done  so  that  some  idea  of  the  behavior  of  the 
cell  is  known.  Potassium  ferrocyanide  is  poured  into  the 
cell  by  means  of  the  funnel.  The  current  is  now  turned  on 
and  the  ions  of  copper  meet  the  complex  ferrocyanogen 
ions.  A  precipitate  is  thus  formed,  the  position  of  which 
depends  upon  the  nature  of  the  porous  cup.  The  solution 
of  potassium  ferrocyanide  is  renewed  every  three  minutes 
to  prevent  the  accumulation  of  alkali  in  the  cell.  This 
membrane-forming  process  is  repeated  for  several  days  at 
a  time  in  the  first  stages  of  the  growth  of  a  cell.  The  cell 
is  then  set  up  with  a  normal  sugar  solution  containing  eight 
hundred  thirty  nine  ten-thousandths  of  a  gram  of  potassium 
ferrocyanide  to  one  hundred  cubic  centimeters  of  solution 
by  weight.  Potassium  ferrocyanide  is  used  with  the  sugar 
solution  to  repair  any  momentary  ruptures.  The  object 
of  setting  a  cell  up  in  this  way  is  to  pack  the  membrane 
as  firmly  as  possible  and  to  fix  it  firmly  in  the  wall  of  the 
cell.  In  addition,  it  ruptures  the  weakest  parts  of  the 
membrane  which  are  to  be  repaired  the  next  time  deposition 
of  membrane  takes  place.  It  is  fully  realized  that  this  small 


amount  of  potassium  ferrocyanide  does  not  produce  a  com- 
plete repair  of  the  ruptures  nor  is  it  believed  that  even  in 
the  finished  cell  is  this  repair  complete;  but  it  is  believed 
that  it  hastens  the  formation  of  a  membrane  that  approaches 
perfection  because  this  repair  takes  place  under  pressure. 
On  the  supposition  that  the  molecule  of  potassium  ferro- 
cyanide completely  dissociates  into  five  ions  in  solution 
"dilute  and  concentrated,"  it  is  considered  that  osmotically 
equivalent  amounts  of  copper  sulphate  and  potassium 
ferrocyanide  are  used.  Consequently,  the  true  osmotic 
pressure  is  not  increased  or  decreased.  A  cell  will  probably 
develop  fifteen  to  twenty  atmospheres  of  pressure  at  this 
stage  of  its  life  history.  It,  however,  would  hardly  be  ex- 
pected to  maintain  a  constant  pressure  for  more  than  twenty- 
four  to  forty  hours. 

Some  approximate  ideas  as  to  the  qualities  of  a  cell  are 
obtained  from  this  trial  measuremnt  which  is  preferably 
carried  on  in  a  constant  temperature  bath.  It  is  quite  de- 
sirable that  the  cell  be  developed  under  uniform  conditions. 
This  statement  is  based  on  experimental  evidence.  No 
claim  is  made  that  it  is  definitely  known  in  what  manner 
the  copper  ferrocyanide  membrane  arranges  itself  in  the  pores 
of  the  cell  but  there  is  certain  definite  evidence  at  hand 
which  has  led  to  conclusions  based  upon  physical  and  closely 
related  analogies  which  will  be  discussed  later.  When  the 
pressure  decreases  markedly,  the  cell  is  taken  down,  washed 
thoroughly  with  water  at  the  same  temperature  as  that 
at  which  it  was  used  during  the  trial  measurement.  It 
is  then  placed  in  a  solution  of  thymol  inside  and  outside 
and  allowed  to  soak  for  several  hours.  This  thymol  solution 
prevents  the  growth  of  penicillium  which  often  infects 
the  cell  in  which  sugar  is  not  completely  removed  and  also 
removes  any  accumulated  salt  from  the  walls  of  the  cell. 
The  purpose  of  removing  the  accumulated  salt  will  be  fully 
discussed  under  the  topic  of  cells  giving  constant  ratios 
lower  than  should  be  expected  under  normal  conditions. 

During  this  first  stage  of  membrane  deposition,  it  is  found 
that  the  resistance  is  very  low  at  the  outset  but  this  increases 


15 

during  the  day,  for  we  often  deposit  membranes  for  hours 
at  a  time  when  first  working  with  a  cell.  The  next  day 
after  shaking  the  resistance  of  the  cell  starts  at  about  the 
same  place  but  soon  increases  very  rapidly,  rising  much 
higher  than  on  the  previous  day.  This  change  takes  place 
repeatedly  and  soon  it  is  found  that  a  certain  definite  maxi- 
mum resistance  is  reached  for  any  particular  cell.  It  must 
not  be  forgotten  that  often  there  are  certain  fluctuations 
in  the  resistance  and  these  fluctuations  are  only  eliminated 
as  the  process  of  membrane  formation  is  continued.  The 
higher  the  temperature,  generally  at  which  the  cell  is  run, 
the  lower  the  resistance.  Cells,  as  a  rule,  whose  membranes 
are  deposited  at  forty  degrees,  do  not  show  as  high  a  resist- 
ance as  those  whose  membranes  are  deposited  at  zero  degrees. 
In  some  cases  the  resistance  of  membranes  has  been  known 
to  exceed  one  million  ohms.  Other  cases  are  found  in  which 
a  cell  shows  low  resistance  immediately  after  it  has  been 
taken  down  from  a  measurement. 

The  membrane  is  subjected  to  this  packing  and  rupturing 
treatment  repeatedly.  Only  trial  measurements  under  uni- 
form conditions  are  made.  The  second  time  a  cell  is  set  up 
for  measurement,  it  begins  to  show  characteristic  traits. 
The  investigator  who  becomes  experienced  with  these  varia- 
tions, can  form  certain  definite  conclusions  as  to  the  relative 
excellency  of  the  cells  as  a  class.  Usually,  at  this  stage, 
imperfections  show  themselves  and  the  cell  takes  a  turn 
for  better  or  worse  at  this  point.  Imperfections  are  due 
to  two  causes.  The  first  cause  of  imperfection  is  a  result  of 
carelessness  in  the  making  of  the  cell.  This  manifests 
itself  in  small  particles  of  iron  or  brass  which  come  from 
the  lathe  which  is  used  in  turning  out  the  cell.  The  clay 
is  green  (unbaked)  and  minute  metallic  particles  adhere 
to  it.  (These  particles  are  thrown  about  by  the  machinery 
which  is  used  for  the  most  part  in  metal  work.)  The  unbaked 
cell  goes  to  the  potter  and  it  is  heated  to  a  temperature, 
sufficiently  high  to  fuse  these  particles.  A  piece  of  metal 
too  small  to  be  seen  with  the  naked  eye  will  produce  a  dark 
spot  a  couple  of  millimeters  in  diameter  when  fused.  This 


i6 

black  spot  serves  as  a  nucleus  about  which  copper  collects. 
Instead  of  a  membrane  of  copper  ferrocyanide  being  formed, 
there  is  produced  a  spot  of  metallic  copper.  Osmotic  activity 
decreases  as  the  spot  increases.  The  cell  is  usually  discarded 
at  this  period  of  its  life  history.  The  second  cause  of  imper- 
fection is  due  to  the  fact  that  the  cell  is  not  placed  in  the 
furnace  at  the  right  temperature  when  it  is  fired.  Small 
cracks  are  produced  and  these  are  not  filled  with  glaze  when 
the  cell  is  retired.  It  is  impossible  to  fill  these  cracks  with 
membrane  of  sufficient  compactness  to  hold  high  pressures. 

The  shortest  period  recorded  of  a  cell  that  gave  a  measure- 
ment is  found  in  the  case  of  a  cell,  Z,  by  name,  which  developed 
into  a  good  cell  in  the  remarkably  short  period  of  thirty- 
eight  hours.  The  usual  period  is  two  or  three  months.  In 
some  cases  a  period  as  great  as  six  months  is  required.  In 
others,  the  cell  has  never  developed  into  a  measuring  cell. 
The  length  of  time  required  to  develop  satisfactory  membranes, 
depends  very  much  upon  the  texture  of  the  cell.  At  present, 
it  can  be  said  that  about  fifty  per  cent,  of  the  number  of 
cells  worked  with  prove  to  be  measuring  cells. 

The  most  interesting  and  important  work  connected 
with  the  measurement  of  osmotic  pressure  now  begins.  It 
is  this  part  of  the  work  which  determines  the  success  of  the 
investigator  in  securing  measurements.  The  cell  is  in  its 
first  stage  of  actual  measurement  and  at  this  time  the  mem- 
brane should  receive  the  greatest  care.  In  order  to  carry 
out  the  work  to  the  best  advantage,  three  constant  tempera- 
ture baths  were  constructed.  These  baths  are  controlled 
automatically  and  keep  temperature  constant  to  within 
a  few  hundredths  of  a  degree  for  periods  of  over  a  day.  These 
baths  are  used  for  the  deposition  of  the  membrane  at  con- 
stant temperature  and  also  to  maintain  constant  temperature 
during  the  period  of  rest  necessary  for  the  cell.  Much  ex- 
perience is  required  on  the  part  of  the  investigator  to  know 
what  treatment  is  most  advantageous  to  the  cell. 

A  systematic  method  of  caring  for  the  cells  is  also  an 
important  factor  in  the  work.  It  has  been  found  advisable 
to  deposit  membrane  in  all  the  cells  for  a  period  of  two 


17 

hours,  twice  during  the  week.  In  addition,  membrane 
is  deposited  in  the  cell  for  about  an  hour  on  the  day  on 
which  the  cell  is  to  be  set  up  for  a  measurement.  The  work 
is  so  planned  that  the  manometer  and  the  cell  are  put  together 
as  quickly  as  possible  after  the  membrane  has  been  deposited, 
with  as  little  variation  of  temperature.  All  the  solutions 
which  in  any  way  are  to  come  in  contact  with  the  cell  are 
kept  at  a  constant  temperature,  the  same  as  that  at  which 
the  measurement  is  made.  No  variations  in  temperature 
are  allowed  to  take  place  in  any  case  where  it  can  be  avoided. 

It  has  been  found  practicable  in  cells  containing  weak 
membranes  to  deposit  the  membrane  at  a  higher  temperature 
than  that  at  which  the  measurement  is  to  be  taken.  The 
most  remarkable  instance  of  such  practice  is  found  in  the 
case  of  cell  R  which  had  given  no  measurements  whatever. 
After  treatment  for  nearly  a  week,  it  was  tried  out  and  gave 
a  satisfactory  measurement.  It  is  now  one  of  the  most 
reliable  cells  in  the  laboratory.  In  order  to  avoid  abrupt 
changes  in  temperature,  the  cell  is  placed  in  a  solution  of 
thymol  of  such  volume  as  to  cause  a  gradual  change  in 
temperature.  Cell  R  had  membrane  deposited  at  40°  C., 
and  then  it  was  placed  in  thymol  water  at  40°  C.  This  is 
now  placed  in  a  25°  bath  and  it  slowly  and  gradually  reaches 
a  temperature  of  25°  because  of  the  large  volume  of  solu- 
tion that  must  change  in  temperature.  It  will  thus  be  seen 
that  a  membrane  may  be  deposited  at  a  temperature  higher 
than  that  at  which  the  measurement  is  to  be  taken  but  the 
reverse  order  cannot  be  carried  out  successfully.  Instances 
in  which  these  facts  are  clearly  brought  out  are  found  in  the 
cases  of  cells  M,  N,  D  and  F,  which  were  used  at  5°.  It 
required  considerable  time  to  develop  them  for  25°  work. 

No  sudden  or  abrupt  changes  are  allowed  to  take  place 
during  the  period  of  rest  of  the  cell.  While  the  cell  is  resting, 
it  is  placed  in  a  glass  vessel  and  supported  by  an  aluminium 
plate  in  which  holes  have  been  drilled.  A  thousandth 
normal  solution  of  thymol  is  placed  on  the  inside  of  the  cell 
as  well  as  in  the  vessel  in  which  the  cells  rest.  The  purpose 
of  this  soaking  is  to  remove  any  sugar  solution  which  may 


i8 

be  occluded  in  the  walls  of  the  cell  or  to  remove  any  accumu- 
lated salt  such  as  potassium  ferrocyanide  or  copper  sulphate. 
The  matter  of  removing  accumulated  salt  is  highly  important 
since  it  may  seriously  affect  the  osmotic  pressure  of  the  solu- 
tion being  measured.  Salt  accumulates  in  the  wall,  due  to 
too  frequent  use  of  the  cell  in  taking  measurements  or  in- 
sufficient soaking. 

The  type  of  cell  used  at  the  present  time  is  made  of  a 
combination  of  clays  from  various  sources.  The  process  of 
making  these  cells  has  been  described  in  an  earlier  paper. 
Kach  cell  has  a  glazed  and  an  unglazed  portion.  The  upper 
part  is  glazed  and  hence  it  is  not  porous.  The  lower  or 
unglazed  portion  is  porous  and  it  is  in  this  portion  that 
the  membrane  is  deposited.  During  the  deposition  of 
membrane  in  the  walls  of  the  cell,  it  was  previously  stated 
that  the  ions  of  the  two  salts  meet  and  form  copper  ferro- 
cyanide. The  current  carries  some  of  the  salt  along  with 
it  into  the  walls  of  the  cell  and  here  by  capillary  action, 
the  solutions  creep  up  under  the  glazed  portion  and  meet 
at  some  point  above  the  lowest  portion  of  the  glaze.  The 
result  is  the  formation  of  a  membrane  at  those  places  where 
the  ions  chance  to  meet.  However,  there  may  not  always 
be  a  meeting  in  this  portion  of  the  cell  and  only  an  accumu- 
lation of  solution  takes  place.  If  a  cell  is  not  soaked  for  a 
considerable  time,  it  is  believed  that  there  is  a  steadily 
increasing  amount  of  salts  left  in  the  cell  wall.  This  accumu- 
lation of  salt  will  cause  a  ratio  to  be  lower  than  should  be 
expected  under  normal  conditions  but  still  it  may  be  very 
constant.  This  may  be  explained  by  the  fact  that  diffusion 
takes  place  counter  to  the  osmotic  activity  and  causes  a 
constant  decrease  of  the  osmotic  pressure.  This  accumulated 
salt  will  diminish  the  apparent  osmotic  pressure  of  a  solution 
within  the  copper  ferrocyanide  membrane.  Since  its  osmotic 
pressure  is  nearly  constant,  it  is  self  evident  that  it  will 
diminish  the  osmotic  pressure  of  any  given  solution  by  a 
constant  amount.  This  is  one  of  the  causes  of  low  ratios 
obtained  sometimes  even  though  there  is  no  loss  in  rotation 
of  the  solution  form  the  cell.  It  will  be  admitted  that  a 


19 

sugar  solution  of  a  certain  definite  concentration  will  yield 
a  constant  maximum  pressure  due  to  osmosis.  When  this 
constant  maximum  is  reached,  water  passes  into  the  cell 
just  as  fast  as  water  passes  out  or  in  other  words  equilibrium 
is  established  but  suppose  that  this  pressure  toward  the 
outside  of  the  cell  is  exerted  with  constant  value,  then  it 
becomes  evident  that  there  is  a  pressure  acting  opposite  to 
osmotic  pressure,  which  will  produce  a  constant  value  below 
the  normal  value  for  that  concentration.  The  amount  that 
this  value  is  below  normal  depends  upon  the  amount  of 
salt  present  and  this  in  turn  determines  the  osmotic  pressure 
counter  to  that  of  the  solution. 

A  second  source  of  low  measurements  is  obtained  from 
imperfect  membranes.  They  are  termed  imperfect  because 
they  do  not  behave  normally.  These  imperfect  membranes 
may  be  found  in  the  cells  that  have  been  in  service  for  a  long 
time  and  seem  to  have  lost  their  osmotic  activity.  Diffusion 
through  such  membranes  is  very  slow  and  in  some  cases 
the  pressure  may  increase  for  six  or  eight  days.  In  the 
meantime,  dilution  has  been  taking  place  and  now  the  cell 
shows  signs  of  diminishing  osmotic  pressure.  Then  again 
little  or  no  change  in  the  pressure  takes  place,  the  pressure 
remaining  the  same  as  that  exerted  upon  it  mechanically. 
No  reliance  can  be  placed  on  measurements  obtained  from 
such  cells.  However,  it  may  be  said  that  such  membranes 
may  prove  to  be  reliable  at  temperatures  higher  than  those 
at  which  the  work  has  been  carried  on.  Another  source 
of  error  lies  in  the  fact  that  the  porous  part  of  the  wall  comes 
in  contact  with  grease  from  the  worker's  hand  in  the  process 
of  setting  up  or  in  some  other  careless  treatment.  These 
cells  cannot  be  repaired  sufficiently  to  produce  an  osmotic- 
ally  active  membrane  because  this  grease  interferes  with 
the  free  passage  of  copper  ions  through  the  wall  unless  they 
are  washed  carefully  with  ether. 

Still  another  source  of  error  is  found  in  the  case  of  sugar 
solution  containing  potassium  ferrocyanide,  which  is  allowed 
to  run  on  the  exterior  of  the  cell.  It  is  then  carelessly  washed 
and  there  is  formed  a  membrane  of  copper  ferrocyanide  on 


20 

the  exterior  of  the  cell  as  soon  as  the  cell  is  placed  in  a  copper 
sulfate  solution.  This  forming  of  a  membrane  on  the  outer 
wall  at  any  one  time  is  small  in  amount,  but  the  effect  is  ac- 
cumulative unless  care  is  taken  in  washing  the  cell  off.  It 
is  found  very  bad  policy  to  remove  this  membrane  by  dip- 
ping in  sodium  potassium  tartrate  solution.  The  proper 
method  of  preventing  such  difficulties  is  to  use  a  tight  fit- 
ting piece  of  thin  rubber  tubing  which  is  slipped  over  the 
porous  part  of  the  cell.  The  overflow  of  solution  is  soaked 
up  by  means  of  drying  paper;  the  cell  is  then  washed  with 
distilled  water  at  a  given  temperature  before  placing  into 
the  copper  sulfate.  If  all  these  little  details  are  carefully 
observed,  there  is  no  reason  why  a  memb ranee  cannot  be 
kept  in  active  condition.  Membranes  which  are  out  of 
sorts  with  the  temperature  at  which  they  are  used  can  in 
some  cases  be  made  active  by  depositing  membrane  in  them 
at  a  temperature  higher  than  that  at  which  they  are  to  be 
used. 

Mention  has  already  been  made  of  the  necessity  of  wash- 
ing the  cells  carefully.  Likewise,  the  vigorousness  with 
which  penicillium  grows  on  almost  any  substance  has  re- 
ceived some  attention  in  earlier  paragraphs.  To  avoid  these 
difficulties  the  copper  sulfate  used  around  the  copper  elec- 
trodes is  made  up  with  thymol  water  which  seems  to  have 
no  effect  upon  the  electrolysis  of  the  solution.  In  one  in- 
stance the  author  found  penicillium  growing  in  copper  sul- 
fate at  twenty  degrees  on  the  electrode  itself.  This  is  only 
further  evidence  concerning  the  fearlessness  with  which 
these  organisms  disseminate  themselves.  In  such  cases  no 
other  result  could  be  expected  than  an  infection  of  the  cells 
by  penicillium.  This  infection  manifests  itself  more  mark- 
edly at  great  dilutions  than  at  those  of  greater  concentra- 
tion for  the  reason  that  penicillium  will  not  grow  in  concen- 
trated sugar  solutions.  It  is  not  known  in  what  manner 
these  organisms  act,  nor  have  any  hypotheses  been  advanced 
concerning  their  action.  It  is  definitely  known  that  some- 
thing does  take  place  to  a  greater  or  less  degree  depending 
upon  the  amount  of  infection.  Manifestations  of  this  diffi- 


21 

culty  was  observed  at  concentrations  up  to  four-tenths  nor- 
mal sugar  solutions.  The  solutions,  taken  from  such  cells, 
possess  a  more  or  less  blue  color  and  in  every  case  there  is 
a  loss  in  rotation  which  means  that  some  change  has  taken 
place  in  the  sugar  solution.  What  this  blue  color  is  due  to 
is  unknown  at  present.  Work  along  this  line  is  being  car- 
ried out  by  the  author.  This  infection,  small  as  it  was, 
continued  for  some  time.  It  then  occurred  to  the  author 
that  a  saturated  solution  of  thymol  would  hasten  the  ex- 
termination of  these  organisms.  This  treatment  was  tried 
on  part  of  the  cells  and  gave  conclusive  proof  as  to  the  ad- 
vantages of  the  treatment.  The  cell  was  filled  with  this 
solution  and  set  in  a  solution  of  the  same  strength.  In 
about  a  week  the  infection  was  eliminated.  Since  the  first 
experience  with  infection  by  penicillium,  the  cells  are  given 
a  treatment  once  every  week  and  no  further  evidence  of  in- 
fection has  appeared.  It  might  be  interesting  to  know 
that  thymol  is  soluble  in  only  small  amounts  of  water  (i  :  1000 
approx.).  This  is  the  degree  of  saturation  which  the  solu- 
tions possess. 

In  earlier  paragraphs  it  was  stated  that  characteristics  of 
cells  would  be  discussed,  and  to  this  our  attention  is  now 
turned.  The  rate  at  which  lithium  sulfate  drives  the  air 
out  of  the  cell  gives  the  investigator  an  idea  as  to  the  porosity 
of  the  cell.  Of  course  the  porosity  depends  upon  the  com- 
pactness of  the  particles  'composing  the  cell.  Burning  at  a 
high  temperature  increases  the  compactness.  This  is  the 
reason  for  speaking  of  the  hard-burned,  non-porous  type. 
A  cell  of  this  type  will  undoubtedly  develop  into  a  measur- 
ing cell  more  quickly  than  the  open,  porous  kind  because 
there  are  a  greater  number  of  plates  to  attach  the  membrane 
to  and  also  the  interstices  are  not  as  large  and,  consequently, 
they  can  be  filled  with  a  membrane  sooner.  The  porous 
type  have  larger  interstices  which  are  to  be  filled  with  mem- 
brane. It  is  a  fact  that  cells  showing  a  high  resistance 
usually  behave  better  than  those  of  lower  resistance,  but 
this  is  no  criterion  as  to  whether  the  cell  will  give  a  measure- 
ment. The  matter  of  resistance  is  only  a  characteristic. 


22 

It  is  not  understood  why  a  cell  shows  these  different  resis- 
tances. Some  membranes  may  show  a  resistance  as  high 
as  a  million  ohms  and  not  give  a  satisfactory  measurement. 
Some  cells  develop  pressure  faster  than  others,  but  the 
exact  reason  of  this  activity  is  not  known.  However,  it  is 
a  function  of  the  membrane.  Good  normal  membranes 
should  hold  a  pressure  of  twenty-five  atmospheres  for  a 
period  of  one  hundred  and  sixty-eight  hours  with  very  little 
variation  in  the  osmotic  pressure.  It  is  a  matter  of  detail 
that  corrections  for  atmospheric  pressure  are  made  in  the 
calculation  of  osmotic  pressure.  If  the  atmospheric  pres- 
sure increases,  the  total  pressure  of  the  cell  would  increase 
and  -vice  versa.  However,  these  changes  do  not  take  place 
at  the  same  rate.  The  total  pressure  of  the  cell  does  not 
follow  the  barometer  accurately. 

In  connection  with  the  work  at  25°,  measurements  last- 
ing over  very  long  periods  of  time  were  carried  out  with 
two  views  in  mind.  First,  the  characteristics  of  a  normal 
membrane  from  the  point  of  view  of  the  length  of  time 
that  it  shows  osmotic  activity,  and,  secondly,  to  show  that 
mechanical  pressure  does  in  no  way  influence  our  final  os- 
motic pressure.  However,  mechanical  pressure  assists  in 
,the  work  by  decreasing  the  length  of  time  necessary  to  reach 
a  maximum  pressure.  In  one  case  an  experiment  lasted  over  a 
period  of  536  hours  with  the  greatest  variation  in  ratio  of 
osmotic  to  gas  pressure  of  two  points  in  the  third  decimal 
place.  After  a  moment's  thought,  it  will  appear  that  this 
is  really  a  remarkable  measurement  considering  the  wide 
variations  of  barometric  pressure  for  a  period  of  two  weeks 
or  more.  Other  experiments  lasting  from  150  to  200  hours 
have  been  carried  on  with  even  better  results.  In  one  of  these 
experiments,  the  greatest  variation  in  ratio  was  only  one 
point  in  the  third  decimal  place  for  a  period  of  192  hours. 
This,  in  brief,  gives  an  idea  of  the  possibilities  of  a  good 
membrane  and  also  a  sufficient  reason  for  retaining  cells 
which  are  of  the  right  texture  to  develop  a  membrane  of  this 
magnitude. 

The  question  may  arise  as  to  the  location  of  this  membrane 


23 

which  is  deposited  in  the  cell.  The  only  answer  to  this 
question  is  indefinite  at  best.  There  are  many  possibilities 
as  to  the  place  that  this  membrane  may  be  formed.  It  all 
depends  upon  the  concentration  of  the  solutions  and  also 
the  place  at  which  the  ions  meet.  Considerable  work  has 
been  done  along  this  line  to  secure  the  proper  adjustment 
of  the  concentrations.  It  is  obvious  that  the  formation  of 
a  membrane  on  the  outer  wall  of  the  cell  can  have  little  or 
no  support  whatever  against  the  pressure  from  within. 
The  fact  is,  that  cells  in  which  the  membrane  has  been  de- 
posited upon  the  inner  edge  of  the  wall  have  been  found  to 
be  uniformly  much  more  active  than  those  in  which  the 
membrane  was  found  within  the  wall.  This  is  to  be  expected 
as  diffusion  takes  place  comparatively  slowly  within  a  por- 
ous body  of  close  texture  and  considerable  density.  If, 
on  the  other  hand,  the  membrane  is  on  the  inner  edge  of  the 
wall,  the  practically  undiminished  concentration  of  the 
solution  within,  and  the  pure  water  circulating  through 
the  porous  wall,  are  separated  only  by  a  thin  membrane, 
and  the  maximum  flow  of  water  will  be  observed.  Ionic 
velocities  and  dissociation  of  electrolytes  play  an  impor- 
tant role  in  fixing  the  position  of  the  membrane.  If  the 
membrane  is  not  close  enough  to  the  wall,  it  will  peel  off 
very  easily,  for  the  reason  that  it  has  no  opportunity  to  at- 
tach itself. 

Through  accident  to  the  cells,  it  has  been  possible  to  ex- 
amine cells  which  possesss  membranes  of  extraordinarily 
good  qualities.  Cell  G,  as  it  was  called,  had  the  bottom 
split  off,  due  to  a  very  sudden  change  in  temperature,  and 
gave  an  opportunity  to  examine  its  membrane.  It  was 
found  that  the  membrane  was  deposited  very  close  to  the 
inner  wall,  vertically  and  horizontally  as  well.  Extending 
into  the  wall  a  fraction  of  a  millimeter,  a  brownish  colora- 
tion is  distinctly  perceptible.  In  addition,  there  was  found 
the  same  brownish  coloration  up  under  the  glazed  portion 
of  the  cell.  This  is  the  situation  of  the  membrane  proper, 
but  there  may  also  be  a  reddish  color  on  the  exterior  of  the 
cell.  It  may  be  said  that  this  is  a  product  of  probable  care- 


24 

lessness  for  the  reason  that  it  may  be  avoided  by  using 
proper  precautions.  It  is  detrimental  because  it  retards 
outward  diffusion  of  water.  It  may  be  prevented  by  keep- 
ing potassium  ferrocyanide  from  coming  in  contact  with  the 
outer  wall,  which  is  filled  with  copper  sulfate  during  the 
process  of  membrane  deposition.  Thus  copper  sulfate  can 
only  be  removed  by  continued  soaking.  The  formation  of 
this  membrane  on  the  exterior  of  the  cell  is  only  further 
evidence  for  the  care  that  should  be  exercised  in  running 
the  cells.  Another  important  observation  in  connection 
with  the  characteristics  of  membranes  is  the  slowness  with 
which  they  respond  to  barometric  changes,  when  the  mem- 
brane has  become  dense,  or  if  excess  mechanical  pressure 
has  been  exerted  on  the  membrane,  it  returns  very  slowly 
to  its  normal  position.  As  a  rule  it  does  not  remain  at  con- 
stant pressure,  but  continues  its  fall,  which  indicates  that 
dilution  is  taking  place  due  to  leakage.  During  this  pres- 
ent year  it  was  necessary  to  go  from  zero  degrees  up  to  twenty- 
five  for  measurements.  Great  difficulty  was  experienced 
in  making  this  change.  It  required  nearly  a  month  and  a 
half  to  get  these  membranes  in  suitable  condition  for  meas- 
urement. 

Cells  become  inactive  due  to  a  large  amount  of  mem- 
brane. They  fail  to  give  measurements,  and  it  is  highly 
important  that  a  method  for  recovering  them  should  be  de- 
vised. Various  reagents  will  dissolve  the  copper  ferro- 
cyanide, but  it  is  also  found  that  they  attack  the  cell  itself, 
rendering  it  valueless  for  deposition  of  membrane  a  second 
time.  Mineral  acids  have  been  tried  with  no  success  what- 
ever. Tart  rate  solutions  do  not  remove  the  membrane 
entirely.  The  only  method  which  is  known  to  be  success- 
ful is  the  electrolytic.  High  voltages  were  tried,  but  it 
was  found  that  the  cell  became  very  hot  due  to  its  own  re- 
sistance. The  voltage  which  seemed  most  suited  to  the 
work  was  obtained  from  twenty  storage  cells  connected  in 
series.  The  danger  of  heating  the  cell  lies  in  the  fact  that 
it  may  crack  if  it  is  not  carefully  watched.  In  the  case  of 
low  voltage  it  is  possible  to  allow  the  process  to  go  on  night 


25 

and  day.  The  copper  collects  on  the  cathode  and  thus  is 
removed  by  dipping  into  nitric  acid.  A  little  tartaric  acid 
is  used  to  add  to  the  conductivity  of  the  solution.  It  has 
been  found  that  about  two  months  are  required  to  remove 
the  membrane.  The  cell  is  then  sent  to  the  potters  and 
retired,  in  a  manner  similar  to  the  first  process.  Membrane 
is  then  deposited  in  the  cell  just  as  in  a  new  cell.  The  same 
amount  of  time  is  necessary  and  the  same  attention  is  needed 
to  develop  this  cell  into  a  measuring  cell.  The  experiment 
has  been  tried  with  cells  "A"  and  "C,"  both  of  which  have 
given  measurements.  The  process  is  being  tried  on  "J" 
and  "K."  If  good  results  are  obtained  from  these  cells 
upon  redeposition  of  membrane,  it  is  conclusive  that  the 
method  is  satisfactory. 

NOTE  i. — During  the  vacation  the  cells  were  placed  in  a 
solution  of  thymol.  No  attention  was  given  them  except 
that  the  solution  of  thymol  was  renewed  at  intervals. 

^Indicates  that  the  maximum  resistance  on  the  day  after 
a  measurement  had  been  taken  was  that  indicated  by  the 
sign  * 

In  the  accompanying  tables,  the  date  on  which  the  deposi- 
tion of  membrane  began  is  indicated  at  the  top  of  each  col- 
umn under  the  name  of  the  cell  in  question.  Under  this, 
the  date  on  which  the  cell  gave  its  first  measurements,  is 
found.  In  the  first  vertical  column  the  days  on  which  the 
cell  was  set  up  for  deposition  of , membrane  previous  to  its 
first  measurement;  in  column  2,  the  number  of  hours  during 
which  deposition  of  membrane  took  place  on  any  given 
date;  third  column,  the  maximum  resistance  for  that  day, 
are  tabulated. 

Looking  over  the  table  for  any  cell,  it  will  be  found  that 
usually  a  minimum  resistance  was  recorded  on  the  day  on 
which  the  cell  was  taken  down  from  a  trial  measurement. 
The  cause  of  this  low  resistance  is  entirely  unknown.  Cer- 
tain hypothesis  might  be  suggested,  but  owing  to  the  fact 
that  the  changes  taking  place  in  the  membrane  cannot  be 
observed,  no  definite  statements  will  be  made.  Another 
feature  brought  out  by  the  tables  is  the  fact  that  some  cells 


26 


Cell  Z. 

Began  deposition  March  10,  '09. 
First  measurement,  Feb.  5,  '09. 


Cell  C3. 

Began  deposition  Oct.  15,  '09. 
First  measurement,  Feb.  23,  '10. 


Date. 

Hours. 

Resistance. 

Date. 

Mar. 

10 

6 

216,000 

Oct.    15 

11 

4 

140,000* 

"       20 

" 

12 

3 

180,000 

"      21 

" 

15 

6 

125,000* 

"      22 

" 

16 

7 

216,000 

"       25 

" 

18 

3 

106  ,000* 

"       26 

" 

19 

4 

60  ,000* 

«       2? 

" 

20 

5 

186,000 

«      29 

* 

22 

6 

220  ,000 

Nov.  15 

« 

23 

8 

188,000* 

"       24 

« 

25 

8 

155  ,000* 

"       29 

" 

26 

8 

290  ,000 

Dec.      1 

i 

29 

4 

160  ,000* 

"         6 

Apr. 

2 

183  ,000 

"       13 

2 

2 

160  ,000* 

Jan.      6 

« 

5 

3 

187  .000 

Feb.    16 

16  measurements 

"      23 

Cell  W. 

Began  deposition  Mar. 
First  measurement,  Oct 


Date. 
Mar.  24 
26 
29 
30 
Apr.      1 
2 
6 
8 
14 
16 
19 
23 
"       24 
May    10 


Oct. 


Hours. 
4 
8 
4 
3 
2 
3 
4 
4 
4 
7 
3 
2 
4 
2 

Note. 
1 
3 
3 
2 
2 
1 


24,  '09. 
19, '09. 

Resistance. 
110,000 
290 ,000 
113,000* 
220 ,000 
486  ,000* 
400 ,000 
140,000* 
160,000 
224 ,000 
160,000* 
140,000 
130,000* 
184,000 
160,000* 

189  ,000 
275  ,000 
565  ,000 
180  ,000* 
280  ,000 
275  ,000* 


Cell  G. 

Began  deposition,  May  20.  '09. 
First  measurement,  Jan.  24,  '10. 


Date. 

Hours. 

Resistance. 

Oct.    15 

1 

375  ,000 

"      20 

2 

290  ,000 

"      21 

2 

140  ,000* 

"      22 

3 

150,000 

"      25 

1 

220  ,000 

"       26 

2 

210,000 

"       27 

1 

183,000* 

"      29 

1 

230  ,000 

Nov.  15 

2 

185,000* 

"       24 

1 

350,000* 

"       29 

1 

357  ,000 

Dec.      1 

1 

1  ,080  ,000* 

"         6 

3 

535  ,000* 

"       13 

3 

560  ,000 

Jan,     6 

3 

275  ,000* 

Feb.    16 

4 

550  ,000 

23 

2 

110,000* 

Cell  h 

Began  deposition, 
First  measurement, 

May  20,  '09. 
Mar.  7,  1910. 

Date. 

Hours. 

Resistance. 

May   20 

3 

60  ,000 

Oct.      9 

3 

285  ,000 

13 

2 

157  ,000* 

20 

2 

387  ,000 

21 

2 

555  ,000 

26 

272  ,000 

29 

380  ,000 

N  v.     9 

380  ,000 

15 

275  ,000* 

22 

550  ,000 

29 

535  ,000 

Dec.    13 

1,120,000 

Jan.      6 

550  ,000* 

"      31 

280  ,000 

Feb.    11 

280,000* 

"       16 

2 

550  ,000 

Mar.     7 

3 

550,000 

Cell  A3. 

Began  deposition,  May  4,  '09. 
First  measurement,  Feb.  12,  '10. 


Date. 

Hours. 

Resistance. 

Date. 

Hours. 

Resistance. 

May 

20 

4 

80  ,000 

May 

4 

3 

140  ,000 

• 

22 

4 

133  ,000* 

" 

6 

3 

160  ,000 

Oct. 

13 

2 

220  ,000 

" 

8 

3 

183,000 

" 

18 

1 

275  ,000 

" 

11 

2 

270  ,000 

u 

20 

2 

194,000* 

u 

13 

3 

220  ,000 

u 

21 

2 

275  ,000 

" 

17 

2 

220  ,000 

" 

27 

j 

224  ,000* 

" 

18 

2 

222  ,000 

Nov. 

9 

2 

265  ,000* 

" 

20 

2 

90  ,000 

Dec. 

4 

2 

355  ,000 

" 

22 

3 

180  ,000 

" 

17 

550  ,000 

Note. 

Jan. 

6 

1 

220  ,000* 

Oct. 

9 

3 

160,000 

22 

2 

365  ,000 

* 

13 

2 

275  ,000 

" 

24 

2 

220,000 

" 

18 

1 

275  ,000 

" 

20 

2 

290  ,000 

« 

21 

2 

278  ,000 

« 

27 

1 

183  ,000 

Nov. 

9 

2 

350,000 

" 

29 

1 

535  ,000 

Dec. 

1 

1 

540  ,000 

Jan. 

6 

3 

550  ,000 

31 

1 

560,000 

Feb. 

11 

1 

280  ,000 

Cell  R. 
Began  deposition,  Feb.  3,  '09. 
First  measurement,  Mar.  21,  '09. 

Cell  V. 
Began  deposition,  Mar.  10,  '09. 
First  measurement,  Nov.  29,  '09. 

Date. 

Hours. 

Resis  tance. 

Date. 

Hours. 

Resistance. 

Feb. 

3 

2 

275  ,000 

Mar.   10 

6 

108  ,000 

5 

3 

365  ,000 

"       11 

4 

110,000 

« 

8 

2 

545  ,000 

"       12 

3 

138  ,000 

u 

10 

3 

297  ,000* 

"       15 

6 

140  ,000 

u 

12 

5 

113,000* 

"       16 

7 

154  ,000 

u 

13 

3 

224  ,000 

"       18 

3 

130  ,000 

a 

16 

2 

355  ,000 

"       19 

4 

155  ,000 

u 

17 

2 

53  ,000* 

"      20 

5 

160,000 

u 

19 

2 

363  ,000 

"       22 

6 

180,000 

u 

25 

6 

285  ,000 

"      23 

8 

100  ,000 

Mar. 

2 

6 

525  ,000 

"       26 

8 

195  ,000 

1 

250  ,000* 

"      29 

4 

125  ,000 

« 

24 

2 

14  ,000* 

"      31 

3 

160,000 

Apr. 

2 

160,000* 

Apr.      1 

2 

160  ,000 

9 

3 

280  ,000 

2 

3 

110,000 

u 

20 

2 

375  ,000 

"         6 

4 

160  ,000 

« 

27 

1 

375  ,000 

8 

4 

186  ,000 

May 

12 

2 

36  ,000 

9 

3 

140  ,000 

22 

1 

265  ,000* 

"       14 

4 

187  ,000 

Note  I. 

"       16 

7 

187  ,000 

Oct. 

9 

3 

565  ,000 

«       24 

4 

170,000 

11 

2 

372  ,000 

Note. 

« 

14 

2 

1,120,000 

Oct.    11 

2 

280  ,000 

Nov. 

4 

2 

550  ,000 

"       13 

2 

280,000 

29 

1 

535  ,000 

"       14 

2 

280  ,000 

Dec. 

9 

2 

333  ,000 

"       15 

1 

560  ,000 

Jan. 
Feb. 

31 
11 

1 
1 

565  ,000 
550  ,000 

Nov.     4 
"         5 

4 
1 

33  ,000 
535  ,000 

Mar. 

2 

1 

98  ,000 

12 

2 

1  ,000  ,000 

" 

21 

1 

28,200 

14  measurements 

Cell  A5. 

Began  deposition,  May  4,  '09. 
First  measurement,  Feb.  28,  '10. 


Cell  P3. 

Began  deposition,  Mar.  10,  '09. 
First  measurement,  Apr.  14,  '09. 


Date.              Hours.            Resistance.                   Date. 

Hours. 

Resistance. 

May     4                  3                  110,000                    Mar.   10 

6 

108  ,000 

"6                  4                   175,000 

11 

4 

160,000 

"8                   3                   110,000 

12 

3 

12  ,000 

"11                   2                   155,000 

15 

6 

30  ,000 

«       14                  4                   140,000* 

16 

7 

135  ,000 

"17                  4                   132,000 

18 

3 

133  ,000 

"       is                  3                   116,000* 

19 

4 

180,000 

«       20                  3                     65,000* 

20 

5 

160  ,000 

«       22                   3                   150,000 

22 

6 

157,000 

Note. 

23 

8 

190,000 

Oct       9                  3                   140,000 

25 

8 

156,000 

"       13                   2                   275,000 

26 

8 

234  ,000 

«       20                  2                   194,000                        «       29 

4 

140,000 

"      21                   2                   185,000                        «      30 

3 

224,000 

"      26                  1                  135,000*                  Apr       i 

2 

187  ,000 

Nov.     1                   2                   157,000                        «         2 

3 

40  ,000 

6                   2                   180,000*                      «         6     - 

4 

185,000 

"       11 

185  ,000                        »         7 

1 

285  ,000 

"       12 

185  ,000                        «         s 

4 

123,000 

350,000                        «       12 

2 

280,000 

Dec.      8 

330  ,000                        «       14 

4 

190  ,000 

"       18 

187,000* 

Jan.    1  1 

232  ,000 

"      31 

187  ,000* 

Feb.    14 

220  ,000 

"      21 

184,000* 

"       25 

200  ,000 

214,000* 

28 

require  a  greater  number  of  hours  to  produce  a  firm  mem- 
brane than  others.  This,  for  the  most  part,  is  due  to  the 
texture  of  the  cell  which  has  previously  been  described 
under  cell  characteristics. 

In  no  case  has  a  cell  given  a  satisfactory  measurement 
previous  to  that  indicated  under  each  cell.  The  resistances 
of  each  cell  are  recorded  every  fifteen  minutes  and  only  the 
maximum  values  are  observed  in  the  accompanying  tables. 
These  cells  have  not  consistently  given  measurements  after 
the  first  time.  Various  causes  have  been  responsible  for 
these  variations.  The  best  cells  may  not  give  more  than 
eight  or  ten  good  measurements  in  a  year  for  the  obvious 
reason  that  each  cell  is  allowed  a  period  of  rest  ranging 
from  one  hundred  and  fifty  to  three  hundred  hours  and  also 
making  due  allowance  for  an  occasional  failure  on  the  part 
of  the  cell  to  respond  to  the  work  required  of  it.  Changing 
from  one  temperature  to  another  also  occasions  considera- 
ble delay. 

It  is  hoped  that  the  carefully  tabulated  variations  of  the 
behavior  of  a  cell  will  throw  some  light  on  the  future  care 
and  treatment  of  the  cells.  It  may  offer  some  means  of 
improving  the  present  methods  of  deposition  and  lead  to  a 
satisfactory  explanation  of  the  fluctuations  observed  in  the 
case  of  any  particular  cell.  Hydrocyanic  acid  has  been 
found  a  satisfactory  means  of  removing  penicillium  from 
the  cell,  while  formaldehyde  is  an  effective  means  of  pre- 
venting the  growth  of  these  organisms  in  the  containing 
vessels  where  measurements  are  taken.  Furthermore,  it 
has  been  found  that  penicillium  uses  up  the  membrane  and 
leaves  a  blue  color.  No  definite  statement  can  be  made 
regarding  the  manner  in  which  it  acts. 


BIOGRAPHY. 

Chester  Newton  Myers  was  born  in  Lansingburgh,  New 
York,  on  November  7,  1884.  His  early  education  was  re- 
ceived in  the  public  schools  of  Valley  Falls,  N.  Y.  June, 
1906,  he  received  the  degree  of  Bachelor  of  Arts  from  Wil- 
liams College.  He  was  then  appointed  instructor  of  Physics 
and  Chemistry  at  the  Cattaraugus  High  School,  which  posi- 
tion he  held  till  entering  Johns  Hopkins  University.  In 
addition  to  holding  the  position  of  instructor,  he  was  assis- 
tant principal  of  the  high  school.  In  October,  1908,  he 
entered  Johns  Hopkins  University  as  a  graduate  student 
in  Chemistry.  In  1909-1910  he  held  a  University  scholar- 
ship. His  minor  subjects  are  Physical  Chemistry  and 
Physics. 


- 


FOURTEEN  DAY  USE 


I  RETURN  TO  DESK  FROM  WHICH  BORROWED 


This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


1956 


